A. Field of the Invention
The present invention is directed toward the field of manufacturing integrated circuits. More particularly, the present invention is related to a method for depositing tungsten-nitride upon an insulator layer.
B. Description of the Background Art
Deposited tungsten nitride has the potential for being conformal and providing good step coverage. Tungsten nitride also serves as an excellent barrier to the diffusion of many metals that are used in integrated circuit metalization processes. Further, the resistivity of tungsten nitride is low in comparison to other metal barriers, such as titanium nitride. Accordingly, it is desirable to use tungsten nitride in several integrated circuit manufacturing applications. Applications in which tungsten nitride is desirable to employ include the formation of diffusion barriers, gate electrodes, and capacitor electrodes.
Traditionally, the deposition of tungsten nitride is achieved by flowing a gaseous mixture including tungsten hexafluoride (WF6) and ammonia (NH3) into a deposition chamber. The chamber contains a wafer onto which the tungsten nitride is to be deposited. The tungsten hexafluoride and ammonia immediately begin to undergo a gas phase reaction to form tungsten nitride. A thermal reaction occurs to combine the nitrogen from the ammonia and the tungsten from the tungsten hexafluoride to form tungsten nitride (W2N).
The above described traditional process for depositing tungsten nitride also results in the formation of contaminant particles in the form of solid byproducts. Several different byproducts have been observed. These byproducts include ammonia adducts of tungsten hexafluoride ((NH3)4WF6), ammonium fluoride (NH4F) and other ammonium complexes. A range of 90 to 300 of these solid byproduct particles having a diameter of 0.2 μm or greater are generated each time tungsten hexafluoride and ammonia are combined in a traditional process to deposit tungsten nitride on an eight inch wafer. Many of these particles become attached to the deposition chamber's interior and eventually cause an increase in the number of defective dice produced by the chamber.
Further, the tungsten nitride that is deposited using the above described traditional process has a polycrystalline structure in which there are many grain boundaries. As a result, the diffusion barrier properties of the tungsten nitride are compromised. In addition, tungsten nitride films deposited by the traditional method tend not to adhere very well to the substrate upon which they are deposited. Also, it is well known that WF6 consumes silicon during the transient state reaction. As such, silicon encroachment into the tungsten nitride layer contaminates the layer.
Therefore, a need exists for a process for depositing tungsten nitride with very few contaminant particles per wafer. It is also desirable for a deposition process for tungsten nitride to provide for a layer of tungsten nitride that is more amorphous than traditionally deposited tungsten nitride. Furthermore, it is desirable for a tungsten nitride deposition process to provide for a thin film that more strongly adheres to an oxide layer than traditionally deposited tungsten nitride. As a result, the diffusion barrier characteristics of the tungsten nitride layer will be enhanced over traditionally deposited tungsten nitride.